Search results for "ylid"
showing 10 items of 1155 documents
1,3-Dipolar cycloadditions with meso-tetraarylchlorins – site selectivity and mixed bisadducts
2017
The 1,3-dipolar cycloaddition reaction of meso-tetraarylporphyrins with nitrones gives isoxazolidine-fused chlorins. Depending on the substitution pattern on the meso-aryl groups and the nitrone, the chlorins can be obtained in high yields (up to 91%). Bacteriochlorin-type bisadducts are also obtained, although in low yield, from the reaction of meso-tetrakis(pentafluorophenyl)porphyrin with N-methyl, N-cyclohexyl or N-benzyl nitrone. The structure of a bis(N-benzyl isoxazolidine-fused) bacteriochlorin was determined by single-crystal X-ray diffraction and rationalized by DFT calculations. To further explore the nature of site selectivity in the formation of bisadducts, isomeric mixed bacte…
Experimental and theoretical study of the [3+2] cycloaddition of carbonyl ylides with alkynes
2012
[EN] The [3 + 2] cycloaddition reaction between carbonyl ylides generated from epoxides and alkynes (phenylacetylene, methyl propiolate, methyl but-2-ynoate and methyl 3-phenylpropiolate) to give substituted 2,5-dihydrofurans was investigated. The effect of indium(III) chloride on the outcome of the reaction was studied in the case of phenylacetylene and methyl propiolate. The thermal reaction between the carbonyl ylide coming from 2,2-dicyano-3-phenyloxirane and both methyl propiolate and methyl but-2-ynoate was theoretically investigated using DFT methods in order to explain the reactivity and regioselectivity observed.
A Close Look to the Oxaphosphetane Formation along the Wittig Reaction: A [2+2] Cycloaddition?
2020
The Wittig reaction between triphenylphosphine methylide and benzaldehyde has been studied both from conceptual and computational approaches. The supernucleophilic character of ylide accounts for the feasibility of the initial nucleophilic attack. The nature of bonding driving the formation of the first oxaphosphetane (OPA) intermediate in such a domino reaction is examined within a topological-based bonding evolution theory perspective. The sequence of the electronic flow associated to the changes in electron density supports a rationalization via two main electronic stages characterizing the single kinetic step: first, the C-C bond formation, which takes place via donation of electron den…
Unveiling the high reactivity of benzyne in the formal [3+2] cycloaddition reactions towards thioamides through the Molecular Electron Density Theory
2020
Abstract The domino reaction of benzyne with thioamide has been studied within the Molecular Electron Density Theory (MEDT) at the MPWB1K/6-311G(d) level. This domino reaction takes place through i) a formal [3 + 2] cycloaddition (32CA) reaction affording an ammonium ylide, and ii) an extrusion of ethylene from this species yielding a dihydrothiazole. Topological analysis of the electron density of benzyne shows its pseudodiradical structure, that is, without any energy cost, changes to a carbenoid one, allowing its participation as electrophile in polar reactions. As a consequence, the formal 32CA reaction does not have an activation enthalpy. Analysis of the changes of electron density al…
A combined experimental and theoretical study of the polar [3+2] cycloaddition of electrophilically activated carbonyl ylides with aldehydes and imin…
2009
International audience; Numerous 2,5-diaryl-1,3-dioxolane-4,4-dicarbonitriles and 2,4-diphenyl-1,3-oxazolidine-5,5- dicarbonitriles have been synthesized by [3+2] cycloaddition reactions between carbonyl ylides generated from epoxides, and aldehydes or imines. In contrast to the use of aldehydes (3,4,5- trimethoxybenzaldehyde, piperonal, 1-naphthaldehyde, indole-3-carboxaldehyde, furan-2- carboxaldehyde and thiophene-2-carboxaldehyde), the reactions performed with imines (N- (phenylmethylene)methanamine, N-(1,3-benzodioxol-5-ylmethylene)propylamine, N-(1,3-benzodioxol- 5-ylmethylene)butylamine and N-(1,3-benzodioxol-5-ylmethylene)benzylamine) proceed diastereoselectively. The effect of micr…
ChemInform Abstract: Ring Expansion of 1,2,3,4-Tetrahydroisoquinolines to Dibenzo[c,f]azonines. An Unexpected [1,4]-Sigmatropic Rearrangement of Nitr…
2014
When the products of a Strecker reaction of 1,2,3,4-tetrahydroisoquinolines with aromatic aldehydes are quaternized with alkyl triflates and subsequently treated with base, a ring expansion to 6,7,8,13-tetrahydro-5H-dibenzo[c,f]azonine-5-carbonitriles takes place. The nine-membered cyclic products can be obtained in good yields (78–89%) in a process involving the [1,4]-sigmatropic rearrangement of a nitrile-stabilized ammonium ylide. The reaction sequence provides a new, simple, and efficient method for the synthesis of these unusual N-heterocycles.
Evidence of a 1,4-dipole intermediate in the reaction of 1-phenyl-4-vinylpyrazole with ptad
1985
Abstract 1-Phenyl-4-vinylpyrazole reacts with 1-phenyl-1,2,4-triazoline-3,5-dione in methylene chloride to form an unstable azetidine (4). An intermediate 1,4-dipole is probably involved since, when the reaction is conducted in acetone, a 1:1:1 adduct (3) is isolated.
Cyclic fatty acid monomers : synthesis and characterization of methyl w-(2-alkylcyclopentyl) alkenoates and alkanoates
1988
Abstract Some 1,2-disubstituted cyclopentanes were synthesized. These were methyl 9-(2-butyl-cyclopentyl)-8-nonenoate, methyl 7-(2-hexyl-cyclopentyl)-6-heptenoate and methyl 5-(2-octyl-cyclopentyl)-4-pentenoate and their corresponding alkanoates. The synthesis involved a Michael addition of alkylmagnesium bromide to an unsaturated cyclic ester. The resulting cis and trans ethyl 2-alkylcyclopentane carboxylate were further converted to the alcohols then to the aldehydes. The aldehydes were condensed with the ylide derived from the (ω-carboxyalkyl)-triphenylphosphonium bromide and methylsulfinylmethide in DMSO to give unsaturated C18 cyclic fatty acid monomers. These cyclic fatty acids were f…
Unprecedented ring cleavage in the reaction of 1-methyl-3-phenacyl benzimidazolium ylide with diethyl azodicarboxylate
2010
The reaction with diethyl azodicarboxylate (DEAZD) of different cycloimmonium ylides derived from pyridinium, quinolinium, isoquinolinium and 1-methylbenzimidazolium bromides (3, 4, 5 and 6) yielded 3-substituted tetraazapentenes (2). In the special case of 1-methyl-3-phenacyl-benzimidazolium bromide (6a), the ring cleavage compound N-[1-[(ethoxycarbonyl)amino]-2-oxo-2-phenylethylidene]-N-formyl-N-methyl-1,2-benzenediamine (7a) was obtained. Its structure was established by X-ray crystallography.
A new model for C–C bond formation processes derived from the Molecular Electron Density Theory in the study of the mechanism of [3+2] cycloaddition …
2016
Abstract The [3+2] cycloaddition (32CA) reactions of the nitrile ylide (NY) with ethylene and with dicyanoethylene (DCE) have been studied using the Molecular Electron Density Theory through DFT calculations at the MPWB1K/6-31G(d) level. The analysis of the electronic structure of NY indicates that it presents a carbenoid structure with an sp 2 lone pair at the carbon atom. While the 32CA reaction with ethylene presents a low activation energy, 6.1 kcal mol −1 , the transition state structure associated with the 32CA reaction of NY with DCE is located 7.5 kcal mol −1 below the reagents, the reaction being completely regioselective. The topological analysis of the Electron Localisation Funct…